Membrane Support Layer Research Articles

Membrane compaction in batch reverse osmosis operation and its impact on specific energy consumption

Reverse osmosis (RO) membrane water permeability is measured under cyclic pressure loading conditions corresponding to batch and semi-batch operation modes. Due to the viscoelasticity of the membrane support layer, compaction effects carry forward across multiple pressurization cycles, with the intracycle behavior stabilizing after a large number of cycles. The average membrane permeability of semi-batch RO systems is lower than that of batch RO, since semi-batch RO spends a larger fraction of its cycle time at higher pressures. The instantaneous permeability in batch RO decreases during the cycle as pressure is increased, but at a lower rate than the steady-state permeability variation with applied pressure. Therefore, the batch permeability values are lower at low pressures and higher at high pressures than the corresponding steady-state values. Since more water is recovered in the initial low-pressure stages of a multi-stage RO system, compaction increases the specific energy consumption of batch RO more than that of staged systems. Other loss mechanisms such as channel and minor pressure losses and high-pressure motor+pump efficiency variation with load further result in batch RO becoming energetically inferior to two- or three-stage RO, especially for low-salinity, high recovery applications.

Modeling Ion Transport across Thin-Film Composite Membranes During Saltwater Electrolysis.

Affordable thin-film composite (TFC) membranes are a potential alternative to more expensive ion exchange membranes in saltwater electrolyzers used for hydrogen gas production. We used a solution-friction transport model to study how the induced potential gradient controls ion transport across the polyamide (PA) active layer and support layers of TFC membranes during electrolysis. The set of parameters was simplified by assigning the same size-related partition and friction coefficients for all salt ions through the membrane active layer. The model was fit to experimental ion transport data from saltwater electrolysis with 600 mM electrolytes at a current density of 10 mA cm-2. When the electrolyte concentration and current density were increased, the transport of major charge carriers was successfully predicted by the model. Ion transport calculated using the model only minimally changed when the negative active layer charge density was varied from 0 to 600 mM, indicating active layer charge was not largely responsible for controlling ion crossover during electrolysis. Based on model simulations, a sharp pH gradient was predicted to occur within the supporting layer of the membrane. These results can help guide membrane design and operation conditions in water electrolyzers using TFC membranes.

Glycine-Modified Co-MOF Pervaporation Membrane to Enhance Water Transporting.

Cobalt-based metal-organic frameworks (Co-MOFs) with a two-dimensional layered morphology have received increasing attention for pervaporation due to their stability and hydrophilic properties. Using amino glycine (Gly) as a cross-linking agent, the Co-MOF ultrathin two-dimensional membrane doped with organic filler sodium alginate (SA) with the "brick-mixed-sand" structure was proposed. Polyacrylonitrile (PAN) was selected as the support layer of the hybrid membrane. The introduction of Gly efficiently solved the nanomaterial stacking problem and controllably adjusted the interlayer spacing between the nanosheets, which demonstrated good performance for ethanol dehydration. The results of this experimental research showed that the total flux of alcohol/water (9:1) separation by Gly-Co-MOF-SA/PAN hybrid membranes reached 1902 g m-2 h-1, which was 67% higher than that of the pure SA membranes. The "brick-mixed-sand" lamellar dense morphology of Gly-Co-MOF not only enhances membrane hydrophilicity but also provides effective channels for the rapid transport of water, which is expected to be used for the dehydration of organic solvents.

EFFECT OF RICE STARCH CONTENT ON TUBULAR ALUMINA MEMBRANE SUPPORT FABRICATED BY AGAR GELCASTING

This study addresses the challenge of fabricating cost-effective tubular ceramic membranes through agar gelcasting. The addition of rice starch as the pore-forming agent in the ceramic membrane support layer, with varying contents from 0 to 6 wt%, was focused on improving the permeability of the tubular ceramic membrane. Scanning electron microscopy (SEM) revealed the co-existence of large pores from starch decomposition and small pores in the form of interparticle voids. When the rice starch was enhanced, the firing shrinkage and apparent porosity increased, and the bulk density decreased. Notably, the tubular ceramic membranes with 6 wt% of the rice starch addition exhibited a permeability of 0.17 Lh⁻¹m⁻²bar⁻¹ under a pressure of 2.5 bar.

Benzenesulfonamide-Functionalized Electrospun Polysulfone as an Antibacterial Support Layer of Thin-Film Composite Pressure-Retarded Osmosis Membrane: Fabrication and Performance Evaluation

Benzenesulfonamide-Functionalized Electrospun Polysulfone as an Antibacterial Support Layer of Thin-Film Composite Pressure-Retarded Osmosis Membrane: Fabrication and Performance Evaluation

Upcycled PVC support layer from waste PVC pipe for thin film composite nanofiltration membranes

Thin-film-composite (TFC) nanofiltration membranes represent the pinnacle of membrane technology in water treatment and desalination. These membranes typically consist of a polyamide (PA) selective layer and a membrane support layer, often constructed from commercially available materials like polyethersulfone (PES). However, there exists an alternative approach that involves the use of different polymers, preferably upcycled waste polymers, as a viable support layer for TFC membranes. Successfully implementing the upcycling of waste plastics into high-value support membranes can make a significant contribution to addressing the issue of plastic waste pollution. One of the primary challenges associated with utilizing upcycled polymers as support layers is the potential impact on the polyamide selective layer of TFC membranes, subsequently affecting their performance in terms of permeability, rejection, and antifouling properties. In this study, we demonstrate the successful fabrication of TFC membranes with a support layer crafted from upcycled waste PVC pipe. We conducted a comprehensive investigation into the effects of upcycled PVC on the structural and physicochemical properties of the polyamide layer. The ultrafiltration (UF) support membranes were fabricated from waste PVC pipe via the nonsolvent induced phase separation (NIPS) method. Subsequently, a polyamide layer was synthesized atop the Upcycled PVC membrane using interfacial polymerization (IP). The physicochemical properties and performance of the TFC membranes with upcycled PVC support layer were compared with membranes with research-grade (RG) PVC and commercial PES support layers. The results unveiled that the TFC membrane with upcycled PVC support layer exhibited higher water permeability (18.2 LMH/bar), in contrast to RG TFC (15.5 LMH/bar) and PES TFC membranes (13.7 LMH/bar). Furthermore, the salt rejection capabilities of the upcycled PVC TFC membrane were competitive and well within an acceptable range.

Step-Nucleation In Situ Self-Repair to Prepare Rollable Large-Area Ultrathin MOF Membranes.

Ultrathin membranes with ultrahigh permeance and good gas selectivity have the potential to greatly decrease separation process costs, but it requires the practical preparation of large area membranes for implementation. Metal-organic frameworks (MOFs) are very attractive for membrane gas separation applications. However, to date, the largest MOF membrane area reported in the literature is only about 100 cm2 . In the present study, a new step-nucleation in situ self-repair strategy is proposed that enables the preparation of large-area (2400 cm2 ) ultrathin and rollable MOF membranes deposited on an inexpensive flexible polymer membrane support layer for the first time, combining a polyvinyl alcohol (PVA)-metal-ion layer and a pure metal-ion layer. The main role of the pure metal-ion layer is to act as the main nucleation sites for MOF membrane growth, while the PVA-metal-ion layer acts as a slow-release metal-ion source, which supplements MOF crystal nucleation to repair any defects occurring. Membrane modules are necessary components for membrane applications, and spiral-wound modules are among the most common module formats that are widely applied in gas separation. A 4800 cm2 spiral-wound membrane modulewas successfully prepared, demonstrating the practical implementation of large-area MOF membranes.

Construction of 1D akaganeite-templated nanochannels in polyamide forward osmosis membrane for high flux separation and nutrient enrichment

To realize nutrient (NO3–-N and PO43−-P) enrichment through FO, this study focuses on tailoring polysulfone (PSF) support layer of TFC FO membrane using 1D akaganeite (Ak) as nano-template to improve the permeance and selective separation of nutrient ions. The incorporation and the subsequent removal of the nano-template from the PSF support layer instantly created porous structures with the desired nanochannel architectures. The separation performance of the resultant e-Ak/TFC membrane is superior to other as-synthesized TFC membranes due to the presence of highly permeable channels, lower membrane tortuosity of support layer and the formation of homogenous polyamide active layer. This restricts the back-diffusion of ions in the support layer, hence improving the effective driving force across the layer. The membrane demonstrated increased water flux from 6.5 for control TFC to 14.1 L/m2∙h for e-Ak/TFC membrane (∼2.2 times higher) along with high selectivity, JW/JS of 0.58 g/L and lower S value. NO3–-N and PO43−-P were effectively enriched in the feed side due to high ion removal efficiencies by the membrane (>97 %) with water reduction of approximately 25 %. We anticipate this work offers an insight into the design of FO membrane that is capable for desalination and enrichment of nutrient in wastewater.

Ceramic membrane with double catalytic layer for efficient peroxymonosulfate activation and dissolved organic matter (DOM) membrane fouling control

Membrane fouling and low removal of dissolved organic matter (DOM) are the main obstacles for the wide application of ultrafiltration membrane technology in water treatment. Herein, we reported the preparation and application of a novel ceramic membrane, which embedded the cobalt oxide in the membrane support layer, and simultaneously loaded the CoAl composite bimetallic oxide on membrane surface layer. The double catalytic layer membrane (CoAl@AM-Co) enabled more efficient DOM removal and membrane fouling mitigation via in situ peroxymonosulfate (PMS) activation during filtration of actual raw water. Compared to the ceramic membrane with only single catalytic layer, the CoAl@AM-Co/PMS system could achieve much higher normalized membrane flux (0.79 vs. 0.63 and 0.49) and TOC removal (87.47 % vs. 58.35 % and 47.16 %); meanwhile, the molecular weight of DOM in the permeate water would also be significantly decreased. The FT-ICR MS results indicated that the total amount of DOM molecules of the permeate was reduced; the DOM with high H/Cwa and low O/Cwa value could be more easily removed, accompanied with the production of DOM with higher oxidation and unsaturation degree. Singlet oxygen and surface-bound radicals were proved to play a critical role in mitigating the membrane fouling by DOM. The design of ceramic membrane equipped with double catalytic layer and its application in advanced water purification were systematically elucidated for the first time in this work, which provided a new pathway for efficient treatment of surface water containing DOM.

Effect of Laser Parameters on Laser-Induced Graphene Filter Fabrication and Its Performance for Desalination and Water Purification.

Laser-induced graphene (LIG) is a low-cost, chemical-free single-step fabrication process and has shown its potential in water treatment, electronics, and sensing. LIG fabrication optimization is mostly explored for dense polyimide (PI) polymers. However, LIG-based filters and membranes for water treatment need to be porous, and additional steps are required to get porous surfaces from PI-based surfaces. Polyethersulfone (PES) porous membranes are cost-effective and are common in water purification as compared to PI; further, the optimization of LIG fabrication on PES-based porous membranes is not explored. So, this study demonstrated the fabrication, optimization, and characterization of LIG with different laser parameters such as power, speed, image density (ID), focusing, laser platforms, and membrane support layer effect on porous PES commercial (UP010) and lab-casted 15% PES (PES15) membranes. The performance of optimized LIG filters was tested for interfacial evaporation (IE)-based desalination in single and stacked layer configuration and water purification applications such as dye removal and disinfection. IE was done in Joule heating (JH) and solar heating (SH) modes, and the UP010-ID7 LIG filter showed the highest JH evaporation rates of ∼1.1, 1.8, and 2.82 kg m-2 h-1 in single, double, and triple stacked configurations, respectively. Using a JH IE setup, the best-performing UP010-ID7 LIG filters have also shown ∼100% removal of methylene blue dye from the contaminated water. Furthermore, all LIG filters showed a complete 6-log bacterial inhibition at the 5 V filtration experiments; at 2.5 V, the optimized LIG filters showed a higher removal than the non-optimized filters. Additionally, the LIGs obtained with the aluminum platform were the best quality. This work demonstrates that laser power, ID, platform, and membrane support are critical parameters for the best-performing PES-LIG filters, and they can be effectively utilized to fabricate PES-based LIG porous surfaces for various energy, environmental, and catalysis applications.

Design Strategies for Forward Osmosis Membrane Substrates with Low Structural Parameters-A Review.

This article reviews the many innovative strategies that have been developed to specifically design the support layers of forward osmosis (FO) membranes. Forward osmosis (FO) is one of the most viable separation technologies to treat hypersaline wastewater, but its successful deployment requires the development of new membrane materials beyond existing desalination membranes. Specifically, designing the FO membrane support layers requires new engineering techniques to minimize the internal concentration polarization (ICP) effects encountered in cases of FO. In this paper, we have reviewed several such techniques developed by different research groups and summarized the membrane transport properties corresponding to each approach. An important transport parameter that helps to compare the various approaches is the so-called structural parameter (S-value); a low S-value typically corresponds to low ICP. Strategies such as electrospinning, solvent casting, and hollow fiber spinning, have been developed by prior researchers-all of them aimed at lowering this S-value. We also reviewed the quantitative methods described in the literature, to evaluate the separation properties of FO membranes. Lastly, we have highlighted some key research gaps, and provided suggestions for potential strategies that researchers could adopt to enable easy comparison of FO membranes.

Fulvic and alginic acid separation during pressure retarded osmosis: Governing effects and fouling mechanisms

In this study, the performance of model foulant (alginate and fulvic acid) separation by pressure retarded osmosis (PRO) was systematically studied. At the various operating conditions tested, fulvic acid had a greater flux decline and power density loss than alginate. The results of membrane resistance test, SEM-EDX images, and the solute diffusion coefficient K demonstrated that fulvic acid was more likely to clog the inside of the porous support layer of the PRO membrane, which would exacerbate the internal concentration polarization (ICP) phenomena. Although model foulants were successfully removed by PRO (with a retention rate of about 95.0%), the presence of either calcium or magnesium ions was detrimental to the fouling process of PRO membranes. According to the XDLVO theory analysis results, the presence of calcium or magnesium ions increased foulant adhesion to the PRO membrane, thereby resulting in membrane fouling. In addition, Pearson correlation coefficient also showed that the hydrodynamic conditions (effective osmotic pressure difference as well as operating hydraulic pressure acting vertically to the membrane and parallel to the membrane cross-flow shear force) had an important effect on the degree of membrane fouling. This is attributed to the influence of the hydrodynamic conditions on the initial influence water flux and thus on the fouling of the PRO membrane.

Photocatalytic thin film composite forward osmosis membrane for mitigating organic fouling in active layer facing draw solution mode

As a high-flux operation mode of thin film composite-forward osmosis (TFC-FO) membrane, active layer facing draw solution (AL-DS) mode suffers from the severe membrane fouling tendency, which is not addressed well. Here, we introduced a photocatalyst (Anatase titanium dioxide, A-TiO2) onto the support layer of TFC-FO membrane via the bonding of polydopamine (PDA) and polytetrafluoroethylene (PTFE), and prepared two photocatalytic membranes, A-TiO2/PDA@TFC and A-TiO2/PTFE@TFC. Compared with the pristine TFC-FO membrane, both A-TiO2/PDA @TFC and A-TiO2/PTFE@TFC had an improved water permeability (10.5 L m−2h−1 and 9.5 L m−2 h−1, respectively) and reduced reverse NaCl flux salt (0.8 g m−2 h−1 and 0.7 g m−2 h−1, respectively) in the AL-DS mode using 1 mol/L NaCl as draw solution and pure water as feed solution. Moreover, in the 16 h fouling experiment using 200 ppm bovine serum albumin (BSA) solution as a representative pollutant, the flux decline rate of both photocatalytic membranes was dramatically alleviated from 39.7% and 21.7% in the darkness to 8.5% and 9.7% under UV irradiation, respectively, indicating a significant anti-fouling capacity of photocatalytic effect. In all, the presence of A-TiO2 endowed membrane with high permeability, high rejection efficiency and excellent anti-fouling capacity under UV spotlight. As bonding agent, PTFE provided the modified membrane with a high photocatalytic effect and high self-cleaning capacity, while PDA increased the membrane permeability and protected membrane against photocatalytic damage. This work provides a simple and feasible method to improve the anti-fouling capacity of TFC-FO membrane in AL-DS mode.

Effects of Operating Conditions on the Performance of Forward Osmosis with Ultrasound for Seawater Desalination

This study investigates the effect of using ultrasound on water flux through a forward osmosis membrane when applied for seawater desalination. A synthetically prepared solution simulating seawater with scaling substances and organic foulants was used. The parameters considered include membrane cross-flow velocity, flow configuration (co-current versus counter-current), direction of ultrasound waves relative to the membrane side (active layer versus support layer), and type of draw solution (NaCl versus MgCl2). The study revealed that applying a continuous ultrasound frequency of 40 kHz was effective in enhancing water flux, especially when the ultrasound source faces the membrane active layer, irrespective of the used draw solution. The highest water flux enhancement (70.8% with NaCl draw solution and 61.9% with MgCl2 draw solution) occurred at low cross-flow velocity and with the ultrasound waves facing the membrane active layer. It was also observed that the use of ultrasound generally caused an adverse effect on the water flux when the ultrasound source faces the membrane support layer. Moreover, applying the ultrasound at the membrane support layer increased the reverse solute flux. For all tested cases, higher water flux enhancement was observed with NaCl as a draw solution compared to the cases when MgCl2 was used as a draw solution.

Flow behavior and mass transfer of humid air across fiber membrane bundles

In the present work, staggered and inline arranged membrane components are modeled to numerically investigate the flow behavior and mass transfer of humid air across the fiber membrane bundles. For the dehumidification purpose, the humid air flows over the outer surface of the composite membrane fibers, and the lumen side of the membrane maintains a negative pressure where the permeated water vapor is removed from the suction port. The study of flow behavior showed that the velocity contours are denser near the membrane outer wall for both configurations, while a fluid stagnation zone is observed in the staggered arrangement. Through the analysis of the flow and concentration fields in the two configurations, it was found that for the fiber membranes with small radius, the inline arrangement possesses more advantages in terms of dehumidification capacity and energy efficiency. Consequently, the effects of the dimension parameters of inline arrangement on the dehumidification performance of membrane bundles were further explored. The results indicated that the increase of tube pitch has a negative effect on the dehumidification rate. In addition, thickening the thickness of the membrane support layer and decreasing the fiber radius are conducive to the dehumidification performance.

Polyethersulfone–Quaternary Graphene Oxide–Sulfonated Polyethersulfone as a High-Performance Forward Osmosis Membrane Support Layer

Polyethersulfone–Quaternary Graphene Oxide–Sulfonated Polyethersulfone as a High-Performance Forward Osmosis Membrane Support Layer

Performance analysis of cross-flow forward osmosis membrane modules with mesh feed spacer using three-dimensional computational fluid dynamics simulations

This study presents a three-dimensional computational fluid dynamics (CFD) model to characterize the effect of mesh feed spacer's geometry on the performance of cross-flow forward osmosis (FO) membranes. The performance of FO membranes against various spacer's geometrical parameters are investigated in terms of permeate water flux, reverse solute flux, concentrative external concentration polarization (CECP) on the membrane, mass transfer coefficient, and longitudinal pressure drop of the feed channel. Also, the membrane support layer is explicitly modeled as a porous medium; the relation between the internal and external concentration polarization phenomena, under different spacer's geometrical variables, is exhibited for different porosities. Our results reveal that the feed spacer's geometrical parameters affect the performance of FO membranes by influencing the volume of the low-circulation or dead zones, and the shear rate on the membrane active layer. The CECP modulus is mainly dominated by the reverse solute flux and the volume of the dead zone on the membrane, while the mass transfer coefficient and the longitudinal pressure drop are more impacted by the exerted shear stress on the membrane. Furthermore, the results of our model demonstrates that the reduction of internal concentration polarization results in an increase in CECP and a magnified impact of the spacer's geometry on the CECP modulus.

Mass transport analysis of a hollow fiber forward osmosis module via two-layer membrane model derived from the irreversible thermodynamics

A two-layer membrane model was applied to a hollow fiber forward osmosis (FO) module for the first time, and its mass transport characteristics were analyzed. This model is a result of applying the irreversible thermodynamics to both the active layer and the support layer of the asymmetric FO membrane. Two membrane properties of the support layer are added as model parameters, namely the solute convective coefficient and the solute diffusive permeability. Actual numerical calculations were performed using the module model including this membrane model. Consistency between the module model and the actual measurements was good in both water flux and solute flux. This model clarified the effect of the support layer structure on FO performance. Iso-water-flux diagrams with the two properties as variables provided an effective means for increasing the FO membrane permeability.

Investigation of dehumidification performance and flow characteristics of wavy vacuum membrane-based dehumidification modules

This work investigates the dehumidification performance of vacuum membrane-based dehumidification with difference wavy membranes. Firstly, this paper constructs four different models of wavy membrane support layers, and proposes their explicit functions. In addition, the accuracy of different turbulence models under wavy boundary condition are compared. Using the verified turbulence model, this paper studies the dehumidification performance of four wavy membrane-based dehumidification modules. Finally, according to the details of flow field, the mechanism behind these dehumidification phenomena are discussed. Results indicate that low-Reynolds number k–ε turbulence model has a higher accuracy than other models in wavy boundary. Wavy membrane does not always increase the dehumidification efficiency, even if it can always increase dehumidification area. When waviness is in the range of 0∼0.06, the dehumidification effect of four wavy membranes are weaker than that of flat membrane, and the flow resistance of four wavy membranes are higher than that of flat membrane. Vertical velocity induced by wavy membrane is the key factor to enhancing dehumidification performance, and a steeper wavy membrane shape at the tail of backflow is beneficial to dehumidification. This work demonstrates the basic dehumidification mechanism of wavy membrane and can provide suggestions for diversified development of vacuum membrane-based dehumidification module.

Effect of pH on membrane fouling during alcohol dehydrogenase immobilization in PES membrane

Fouling-induced enzyme immobilization is a technique to immobilize enzyme by positively manipulating the knowledge of membrane fouling. In this study, Alcohol dehydrogenase (ADH) (EC 1.1.1.1) was immobilized in the support layer of ultrafiltration PES membrane at different solution pH (acid, neutral and alkaline). ADH catalyses formaldehyde (CHOH) to methanol (CH3OH) and simultaneously oxidised nicotinamide adenine dinucleotide (NADH) to NAD+. The initial feed amount of enzyme is 3.0 mg. The objective of the study aims at the effect of different pH of feed solution during enzyme immobilization, in terms of permeate flux, observed rejection, enzyme loading and fouling mechanism. The results showed that, pH 5 holds the highest enzyme loading which is 65% while pH 7 holds the lowest at 52% out of 3.0 mg as the initial enzyme feed. The permeate flux for each pH decreased with increasing cumulative permeate volume. The observed rejection is inversely correlated with the pH where increase in pH will cause a lower observed rejection. The fouling model predicted that irreversible fouling occurs during enzyme immobilization at pH 7 with standard blocking mechanism while reversible fouling occurs at pH 5 and 9 with intermediate and complete blocking, respectively.